It is true that outragiously high penal tax rates (say 90%) will result into avoidance. However in this situation cutting taxes to 88% from 90% is not going to make much of a difference. Cutting from 90% to 40% will make a difference.

Unfortunately there is no evidence that cutting taxes by small amount (say 1% or 2%) makes any difference to revenues all else being equal.

The single biggest factor influencing tax revenues is the state of the economy. As economy rises tax revenues rise. As economy falls tax revenues fall.

Small changes in marginal tax rate by themselves make very little change to this big picture rule. They may have have secondary effect in that people may feel happy and rising confidence results into some extra economic growth which results into some more incremental tax revenue. However this effect should be small.